Synucleinopathies, including Parkinson's disease and dementia with Lewy bodies, are common aging-dependent neurodegenerative diseases associated with neuronal aggregation of a-synuclein. An in vivo rat synucleinopathy model delineated early key pathological changes preceding overt neuronal degeneration. These may represent critical pathophysiological changes potentially causal to disease progression, without being confounded by cell death-related events. I hypothesized that these pathways perturbed in the pre-degenerative stages are important contributors to the pathogenesis of synucleinopathies, and will yield novel targets for disease-modifying therapies. Two complementary in vitro models will be used to determine the relationships between these pre-degenerative changes and a-synuclein toxicity. Over expressing human a-syn in yeast recapitulates cellular defects seen in the human synucleinopathies, yielding insights into the path biology caused by a-syn misfolding and creating a model amenable to high throughput analyses. Taking advantage of unparalleled genetic tools available, I will use the yeast model to establish causal relationships between these changes and a-syn-dependent cytotoxicity, and to investigate the mechanistic underpinning of such connections when established. Second, I will characterize induced pluripotent stem (iPS) cells derived from familial a-synucleinopathy patients including the A53T and multiplication (duplication, triplication) mutations of a-syn. The recent groundbreaking discovery enabling reprogramming of human somatic cells into pluripotent iPS cells offers an unprecedented approach to the study of human diseases. These cells can be robustly differentiated into neurons, providing a highly relevant context in which to validate and extend findings from the rat AAV and yeast synucleinopathy models, and to generate novel pre-degenerative changes using unbiased gene expression profiling. The multi- model approach using yeast, rat and human iPS cells will facilitate the validation of important pathogenetic pathways, offering novel therapeutic targets for drug development and other therapeutic strategies.